Conventional golf balls can be divided into two general types or groups: two piece balls or three piece balls, the latter including wound balls. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Balls having a two piece construction are generally most popular with the average recreational golfer because they provide a very durable ball while also providing maximum distance. Two piece balls are made with a single solid core, usually formed of a crosslinked rubber, which is encased by a cover material. Typically the solid core is formed of polybutadiene which is chemically crosslinked with zinc diacrylate and/or similar crosslinking agents and is covered by a tough, cut-proof blended cover. The cover is generally formed of a material such as SURLYN.RTM., which is a trademark for an ionomer resin produced by DuPont. The combination of the core and cover materials provide a "hard" ball that is virtually indestructible by golfers. Further, such a combination imparts a high initial velocity to the ball which results in improved distance. Because the materials of which the ball is formed are very rigid, two piece balls have a hard "feel" when struck with a club. Likewise, due to their hardness, these balls have a relatively low spin rate which provides greater distance.
At the present time, the wound ball remains the preferred ball of the more advanced players due to its spin and feel characteristics. Wound balls typically have either a solid rubber or liquid center core around which many yards of a stretched elastic thread or yarn are wound. The wound core is then covered with a durable cover material such as a SURLYN.RTM. or similar material or a softer cover such as Balata or polyurethane. Wound balls are generally softer and provide more spin than non-would balls, which enables a skilled golfer to have more control over the ball's flight and final position. Particularly, with approach shots into the green, the high spin rate of soft, wound balls enables the golfer to stop the ball very near its landing position.
Manufacturers place a great deal of emphasis on producing golf balls that consistently achieve the highest possible initial velocity without exceeding the United States Golf Association's (USGA) limit of 77.7 m/s (255 ft/s) when struck with a driver with a clubhead speed of 39.6 m/s (130 ft/s). In an effort to meet the demands of the marketplace, manufacturers strive to produce golf balls having initial velocities as close as possible to the USGA initial velocity maximum, and yet maintain an acceptable feel and compression.
A number of patents have been issued which are directed towards modifying the properties of a conventional two piece ball by altering the typical single layer core and single cover layer construction to provide a multi-layer ball having such as a dual cover layer, dual core layer and/or a ball having a mantle layer disposed between the cover and the core. The inventions disclosed in the prior art patents are directed towards improving a variety such golf balls' physical properties and "in-play" characteristics.
Several patents are directed towards improving the carry distance of such balls. For example, U.S. Pat. No. 4,863,167 relates to a three piece solid golf ball having increased flight distance, wherein the ball has a center portion and an outer layer formed from a rubber composition, wherein the outer layer is harder than the center portion and further contains a gravity filler so as to impart a higher specific gravity to the outer layer than that of the center portion. U.S. Pat. No. 5,184,828 relates to a solid three-piece golf ball having improved rebound characteristics and carry distance while maintaining an adequate spin rate, wherein these characteristics are obtained by controlling the size of the polybutadiene inner core and outer layer as well as their specific gravity and hardness. According to the '828 patent, the key to obtaining the desired rebound characteristics is that the maximum hardness (42-62 Shore D) must be located at the interface between the core and the mantle and the hardness must then decrease both inwardly and outwardly. U.S. Pat. No. 4,714,253 is also directed towards a three-piece golf ball having an excellent rebound coefficient. This golf ball has a core with a Shore C hardness of 57-80 in its center, but not more than 83 at a distance between 5-10 mm from its center and an outer layer with a Shore C hardness of 70-83.
Additionally, there are a number of patents directed towards improving the spin, click and feel of solid balls while maintaining the distance provided by the solid construction. For example, U.S. Pat. No. 5,072,944 discloses a three-piece solid golf ball having a center layer and an outer layer which are prepared from a rubber composition, wherein it is desirable that the center core layer is softer than the outer layer, the layers having a hardness (Shore C) of 25-50 and 70-90, respectively.
U.S. Pat. No. 4,625,964 relates to a solid golf ball having a polybutadiene rubber core of a diameter not more than 32 mm, a polybutadiene rubber intermediate layer having a specific gravity of lower than that of the core material, and a cover. U.S. Pat. No. 4,650,193 is directed towards a solid golf ball having a core comprising a central portion and an integral outer layer, wherein the core is a curable elastomer such as polybutadiene which is treated with a cure altering agent to soften an outer layer of the core, to produce a central layer with a hardness (Shore C) of greater than 75 and an outer layer with a hardness (Shore A) of less than 80.
U.S. Pat. No. 4,848,770 discloses a non-wound three-piece golf ball which includes a core of a highly filled synthetic rubber or polymeric material, an intermediate mantle of an unfilled synthetic rubber and a cover. The core and intermediate mantle have a hardness of between 50-95 Shore D. U.S. Pat. No. 5,002,281 is directed towards a three-piece solid golf ball which has an inner core having a hardness of 25-70 (Shore C), an outer shell having a hardness of 80-95 (Shore C) and a cover. Further, the specific gravity of the inner core must be greater than 1.0, but less than or equal to that of the outer shell, which must be less than 1.3.
The prior art discloses a variety of materials other than polybutadiene for use as intermediate layers. For example, U.S. Pat. No. 5,253,871 concerns a golf ball having a three piece structure comprising an elastomer core, an intermediate layer of a thermoplastic material containing at least 10% of ether block copolymer, preferably blended with an ionomer, and a thermoplastic cover. U.S. Pat. No. 5,681,898 is directed to a multilayer golf ball having a conventional polybutadiene core, an ionomer cover and an intermediate layer formed from a blend of an ethylene methacrylic acid copolymer and a vulcanizate formed from polybutadiene and a peroxide curing agent. U.S. Pat. Nos. 5,439,227 and 5,556,098 both disclose multilayer golf balls which have a conventional polybutadiene core, conventional covers and an intermediate layer formed from a polyetherester block copolymer filled with zinc oxide and optionally blended with an ionomer.
Further, there are also several patents which are directed to golf balls having multiple cover layers. For example U.S. Pat. No. 4,431,193 relates to a golf ball having a multilayer cover wherein the inner layer is a hard, high flexural modulus ionomer resin and the outer layer is a soft, low flexural modulus ionomer resin, and wherein either or both layers may comprise a foamed ionomer resin. U.S. Pat. No. 5,314,187 also relates to golf balls having a multiple layer cover, wherein the outer layer is molded over the inner layer and comprises a blend of balata and an elastomer and the inner layer is an ionomer resin. U.S. Pat. No. 4,919,434 is directed towards a golf ball having a cover which comprises an inner layer and an outer layer each of which comprise a thermoplastic resin, preferably the layers comprise of materials that are capable of fusion bonding with each other.
However, none of the patents discussed above disclose a multilayer ball which employs the materials and has the improved physical properties as disclosed herein.